1. Field of the Invention
The present invention relates to a DC to DC (i.e., DC-DC) converter module in which various components, including a switching element, are mounted on a magnetic substrate that incorporates magnetic elements, including a smoothing choke and a transformer among main components, and that serves as a component carrying substrate.
2. Description of Related Art
Various typical non-isolated DC-DC converter circuits and current waveforms of portions thereof are illustrated in FIGS. 1 to 3.
FIG. 1(A) is a circuit diagram of a step-down DC-DC converter 11 having an input terminal IN connected to an input voltage source 9. FIG. 1(B) illustrates waveforms of currents Ia and Ib illustrated in FIG. 1(A). FIG. 2(A) is a circuit diagram of a step-up DC-DC converter 12 having an input terminal IN connected to an input voltage source 9. FIG. 2(B) illustrates waveforms of currents Ia and Ib illustrated in FIG. 2(A). FIG. 3(A) is a circuit diagram of an inverting DC-DC converter 13 having an input terminal IN connected to an input voltage source 9. FIG. 3(B) illustrates waveforms of currents Ia and Ib illustrated in FIG. 3(A).
As illustrated in FIG. 1(A), the step-down DC-DC converter includes a switching portion 21, an input capacitor Ca disposed adjacent to an input side thereof, and an output capacitor Cb disposed adjacent to an output side thereof. The switching portion 21 contains a switching element Q, a diode (i.e., flywheel element) D, and a smoothing choke Lb.
For the step-down DC-DC converter, as illustrated in FIG. 1(B), the input current Ia of the switching portion 21 exhibits a discontinuous waveform in which a rectangular pulse current flows when the switching element Q is in an ON state. The output current Ib of the switching portion 21 exhibits a continuous waveform containing ripples.
As illustrated in FIG. 2(A), the step-up DC-DC converter includes a switching portion 22, an input capacitor Ca disposed adjacent to an input side thereof, and an output capacitor Cb disposed adjacent to an output side thereof. The switching portion 22 contains a switching element Q, a diode (i.e., flywheel element) D, and a smoothing choke La.
For the step-up DC-DC converter, as illustrated in FIG. 2(B), the input current Ia of the switching portion 22 exhibits a continuous waveform containing ripples. The output current Ib of the switching portion 22 exhibits a discontinuous waveform in which a rectangular pulse current flows when the switching element Q in an OFF state.
As illustrated in FIG. 3(A), the inverting DC-DC converter includes a switching portion 23, an input capacitor Ca disposed adjacent to an input side thereof, and an output capacitor Cb disposed adjacent to an output side thereof. The switching portion 23 contains a switching element Q, a diode (i.e., flywheel element) D, and a smoothing choke Lab.
For the inverting DC-DC converter module, as illustrated in FIG. 3(B), the input current Ia and the output current Ib of the switching portion 23 both exhibit a discontinuous waveform in which a rectangular pulse current flows.
An isolated DC-DC converter module circuit is illustrated in FIG. 4. FIG. 4(A) is a circuit diagram of a forward DC-DC converter. FIG. 4(B) is a circuit diagram of a flyback DC-DC converter.
As illustrated in FIG. 4(A), the forward DC-DC converter includes a switching portion 24, an input capacitor Ca disposed adjacent to an input side thereof, and an output capacitor Cb disposed adjacent to an output side thereof. The switching portion 24 contains a switching element Q, a transformer T, diodes Da and Db, and a choke coil Lc.
For this forward DC-DC converter, as similar to the step-down DC-DC converter, the input current Ia of the switching portion 24 exhibits a discontinuous waveform in which a rectangular pulse current flows when the switching element Q is in an ON state, and the output current Ib of the switching portion 21 exhibits a continuous waveform containing ripples.
As illustrated in FIG. 4(B), the flyback DC-DC converter includes a switching portion 25, an input capacitor Ca disposed adjacent to an input side thereof, and an output capacitor Cb disposed adjacent to an output side thereof. The switching portion 25 contains a switching element Q, a transformer T, and a diode Da.
For this flyback DC-DC converter, as similar to the inverting DC-DC converter, the input current Ia of the switching portion 25 is pulsed, and the output current Ib of the switching portion 25 is a discontinuous waveform in which a rectangular pulse current flows when the switching element Q is an OFF state.
A DC-DC converter module configured in a magnetic insulated substrate with the aim of reducing the size of the DC-DC converter is disclosed in Japanese Unexamined Patent Application Publication No. 2004-343976.
For example, in the case of the step-down DC-DC converter and the forward DC-DC converter, the input current input into the switching portion is pulsed, as illustrated in FIG. 1(B). If this input pulse current flows through wiring between the input voltage source and the main body of the DC-DC converter, a problem arises in which noise (e.g., fundamental noise and harmonics noise of the pulse current) occurs from there. To address this, the pulse current is supplied from the input capacitor Ca, and the current path is completed within the module.
However, when the DC-DC converter module is implemented on a circuit board of an electronic device, the input voltage source and the DC-DC converter module may be spaced apart. As a large proportion of the above pulse current flows into the input capacitor Ca, and as the pulse current Ic also flows from the input voltage source 9 to the DC-DC converter 11, if the gap between the input voltage source and the DC-DC converter module is relatively large, the size of the loop of the current IC flowing through the wiring therebetween is large. This leads to an increase in occurrence of electromagnetic noise, and the increase is a problem.
For the step-up DC-DC converter, as illustrated in FIG. 2(B), the output current Ib output from the switching portion is pulsed. Thus, the output capacitor Cb is provided such that the pulse current can be prevented from flowing into the loading side and such that the output voltage can be prevented from having a ripple.
However, to enable a large proportion of the above pulse current to flow into the output capacitor Cb, it is necessary for the output capacitor Cb to have a large capacity and low resistance, so there is a limit to the use of only a capacitor.
The inverting DC-DC converter and the flyback DC-DC converter have both of the above-described problem occurring in the step-down DC-DC converter and that in the step-up DC-DC converter.
Japanese Unexamined Patent Application Publication No. 2004-343976 relates to a DC-DC converter module in which various components, including a switching element, are mounted on a magnetic substrate that incorporates merely a choke component and that serves as a component carrying substrate. Japanese Unexamined Patent Application Publication No. 2004-343976 does not describe a structure for reducing noise.
One approach to solving the above problems is to use a component resistant to allowing a radio-frequency content to pass therethrough, such as an inductor or a ferrite bead. This approach can prevent noise caused by the pulse current from leaking out. However, because of the necessity to use such an additional antinoise component, the problem of increasing a footprint and cost remains.